This invention relates to sighting devices for projectile launchers, particularly sighting devices using the apparent height of a target at the sighting device to sight the target and, in so doing, automatically aim the launcher to facilitate accurate delivery of projectiles at the target.
Sighting devices are widely used in conjunction with projectile launchers, such as target guns and archery bows. Use of sighting devices is generally desirable so as to facilitate accurate delivery of the launched projectile, e.g., bullets, pellets, arrows or the like, at a target located within a range of distances from the launcher. In archery, for example, sighting devices generally are desirable for use by an archer in properly selecting the angle at which the arrow is launched, that is, in aiming the bow. The selection of the launch angle is a difficult task in archery as it requires consideration of numerous factors, including the target's position, gravity, the arrow's launch velocity, and other environmental and launch conditions affecting the trajectory of the arrow in its flight from the bow to the target. Sighting devices are employed to account for one or more of such factors such that, when the archer aligns the target in a sighting element, e.g., cross-hairs or a pin, the sighting device sets the launch angle and, thereby, the trajectory. Sighting devices are similarly employed in using other projectile launchers.
Various sighting devices have been employed for use with archery bows. One type of sighting device relies on the archer determining the target's distance so as to adjust manually the sighting device for that distance or to select one of a plurality of sighting elements, such elements calibrated for respective distances. This type of sighting device, however, is subject to significant limitations. For example, the archer determines the distance either using guesswork or using a range-finder separate from the sighting device. The former approach introduces undesirable inaccuracy; the latter approach one or more undesirable additional steps. In addition, use of multiple pins not only requires determination of the target's distance, but generally also (i) requires the archer to calibrate the pins, that is, to fix their relative positions, through trial-and-error and (ii) limits the archer's accuracy to the respective distances associated with the finite number of pins. This type of sighting device can be found in Pizzuti U.S. Pat. No. 2,669,023, Frydenlund U.S. Pat. No. 3,487,548, Perry U.S. Pat. No. 4,224,741, Closson U.S. Pat. No. 4,541,179, Godsey U.S. Pat. No. 5,092,052 and Jorlov U.S. Pat. No. 5,117,804.
Another type of sighting device incorporates a conventional optical range finder, e.g., a coincident image optical range-finder, together with a separate sighting element. The archer aligns the images in the range-finder and, in so doing, the sighting element is moved to the proper position for launching the arrow. This type of sighting device is also subject to significant limitations. For example, an undesirable additional step is required in that the archer must first determine the range using the range-finder and then align the target in the sighting element. That is, the archer is required to shift sighting of the target from the range-finder to the sighting element. This shifting generally is undesirable, but it is particularly undesirable in bow hunting where economy in all movement, including sighting, is important. In addition, this type of sighting device, in employing precision optics, introduces problems with optical damage, maintenance and loss of calibration, particularly so when subject to the rigors of bow hunting. This type of sighting device can be found in Saltzman U.S. Pat. No. 4,473,959 and Oligschlaeger U.S. Pat. No. 4,979,309.
Accordingly, there is a need for an improved sighting device that overcomes the limitations of conventional sighting devices.